Along with increase in technological development and demands of mobile devices, the demand for a battery as an energy source has remarkably increased and, accordingly, a large amount of research has been conducted into a battery that meets various demands.
Representatively, there is high demand for a prismatic rechargeable battery and a pouch-type rechargeable battery which have a small thickness to be applicable to products such as mobile phones in terms of a battery shape and there is high demand for a lithium rechargeable battery such as a lithium ion battery and a lithium ion polymer battery with high energy density, discharge voltage, and output stability in terms of a material.
A rechargeable battery is classified according to a structure of an electrode assembly with a positive electrode/separator/negative electrode structure and, representatively, there are a jelly roll (winding type) electrode assembly configured by winding long-sheet type positive and negative electrodes with a separator interposed therebetween, a stack-type electrode assembly configured by sequentially stacking a plurality of positive and negative electrodes which are torn in units of predetermined sizes and between which a separator is interposed, and a stack/folding-type electrode assembly configured by winding bi-cells or full-cells in which a predetermined unit of positive and negative electrodes are stacked with a separator interposed therebetween.
A stack-type electrode assembly is configured by sequentially stacking structures in which a separator is interposed between a positive electrode with a positive active material coated on opposite surfaces of a positive current collector and a negative electrode with a negative active material coated on opposite surfaces of a negative current collector.
In this case, a plurality of positive and negative electrode taps configured with an uncoated area on which an active material is not coated protrude from one-side end of positive and negative electrodes to be electrically connected to positive and negative electrode leads configuring an electrode terminal of a battery, respectively.
These positive and negative electrode taps are formed via notching in which a predicted portion to be coupled to an electrode lead at an uncoated area with no active material coated thereon protrude from a current collector. Positive and negative taps that protrude via notching may be densely coupled to be connected to positive and negative electrode leads, respectively.
In this regard, FIG. 1 schematically illustrates a general structure of a conventional stack-type electrode assembly and a coupling type between electrode taps and electrode leads.
Referring to FIG. 1, a plurality of positive electrode taps 21 that protrude outward from a positive electrode 20 of an electrode assembly 10 and on which a positive active material is not coated and a plurality of negative electrode taps 31 that protrude outward from a negative electrode 30 in the same direction as the positive electrode taps 21 may be connected to, for example, a positive electrode lead 40 and a negative electrode lead 50 in the form of welding portions that are integrally coupled via welding, respectively.
However, in the conventional electrode assembly, a negative active material is coupled to a lithium ion to expand during a charge procedure or gas is generated via decomposition of an electrolyte solution or an electrochemical reaction during a repeated charge and discharge procedure to cause a swelling phenomenon in which a battery swells. Due to stress generated in this case, the volume and thickness of an electrode assembly are changed and, particularly, an outer appearance is also deformed and, furthermore, there is a problem in that performance of a battery remarkably deteriorates.
In addition, when a high-capacity material such as transition elements as well as Si metal is applied to a negative active material to develop a battery cell with a high energy density, very large volume expansion compared with a graphite-based active material is caused and, thus, the above problems are more serious.
Accordingly, there has been a need for an electrode assembly with a structure for implementing a battery with a high energy density and, simultaneously, preventing a swelling phenomenon and electrode deformation due to charge and discharge.